Voltage Divider Calculator

The voltage divider is one of the first circuits every electronics hobbyist, student and engineer learns, and one of the most useful, because it does something you need constantly: it takes a voltage and scales it down to a smaller, precise fraction. It is nothing more than two resistors in series across a supply, with the output tapped from the point between them, yet that simple arrangement is everywhere, from setting reference voltages and biasing transistors to reading a sensor, scaling a signal so it fits a microcontroller's input range, or making a potential divider for measurement. This calculator works out the output for you from three values: the input voltage and the two resistor values, R1 on top and R2 to ground. Enter them and it returns the output voltage taken across R2, along with the current flowing through the divider, updating instantly as you change any value so you can dial in the exact ratio you need. The output depends only on the ratio of the resistors, so the same fraction can be made with small or large resistors, but the scale you choose matters in practice: larger values draw less current and waste less power, while smaller values are stiffer and less affected by whatever you connect to the output. Seeing the current as well as the voltage helps you balance those trade-offs and avoid overloading a supply or sagging the output under load. Whether you are designing a circuit, troubleshooting one on the bench, or learning how series resistors share a voltage, this gives a fast, accurate answer. The formula and a worked example are set out below so you can understand and apply it confidently yourself.

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